Take a look at this page from an early 9th century French manuscript copy of Expositio Psalmorum by the 6th century Roman writer Cassiodorus:[1]

Just you look at this wonderful initial:

No, seriously, look:

Alongside three imaginary and highly stylized monsters, we find a surprisingly accurate sketch of an elephant![2][3] The depiction is faithful enough for us to identify the species: the iconic small floppy ears could only belong to an Asian elephant.

To understand just how unsual this is, you only have to see other pre-Renaissance examples:[4]

The thing is, as you can guess, elephants were not a frequent sight in medieval Europe; nor was there a statue, painting or carving of an elephant, made by a person who actually saw one. All they had to base their images on were short, vague, and often inaccurate textual descriptions. Ironically, Cassiodorus himself wrote about elephants several times, including a passage in Expositio Psalmorum. Towards the end of the book, when explaining why, in Psalm 44, ivory houses are appropriate for virtuous women, he writes:[5]

The elephant to whom these tusks belong is said to be most chaste; among quadrupeds he is endowed with the highest intelligence, his intercourse with his mate is disciplined, and he enjoys no second spouse.

In one of his letters he goes into much more detail, saying among other things:[6]

these animals live in the flesh more than a thoudsand years

The living elephant … cannot get up again unaided. This is because it has no joints in its feet.

its breath … is said to be a remedy for the human headache.

So, what about the nicely delineated head in St-Denis manuscript? Actually, the very fact, that it is so much better than anything else of the period, suggests that the artist drew it from personal experience. Which immediately identifies the animal.

The only elephant to reach Europe, between the fall of the Roman Empire and until the 13th century, was Abulabaz, owned by the great Charlemagne. A gift from the caliph of Baghdad, Harun al-Rashid, Abulabaz lived at the emperor’s court from 802 to 810, where he was regularly exhibited. Understandably, he generated a lot of interest and excitement, so, it’s quite possible that the Expositio‘s artist made a journey to Aachen or Augsburg to see the mythical creature.

So, what we have here is probably a sketch of Charlemagne’s pet elephant. Which is quite something, considering no contemporary portrait of the emperor survives.

An exhaustive treatment of the subject can be found in: George C. Druce, The Elephant in Medieval Legend and Art,
Journal of the Royal Archaeological Institute, Volume 76, London, 1919. scans at The Medieval Bestiary